The seminar of the Astro & Theory Section takes place Fridays normally on Wednesdays in E3-128 and on zoomD5-106, starting normally at 12.15
- 09.10.2020, David Mota (UiO): Cosmological and Astrophysical probes of Gravity Theories beyond General Relativity
Abstract: Several modifications to general relativity have been proposed with the aim to explain the nature of dark energy and the accelerated expansion of the Universe. In this talk I will review the present status of modified theories of gravity in the light of astrophysical probes of gravity in the weak-field regime, ranging from stars to cosmological scales. I begin by setting the scene for how theories beyond General Relativity are expected to behave in the different astrophysical systems, as well as their cosmological signatures. With these in hand, I present a range of observational tests with an eye to using the current and next generation of observations for tests of gravity. In particular, I will show how physical observables of the non-linear regime of structure formation are promising probes to constraining theoretical models in the nonlinear dynamics of stars, galaxies, clusters and large scale structure.
- 23.10.2020, Tim Linden (Stockholm U/OKC): Thermal WIMPs on the Brink
Abstract: Weakly Interacting Dark Matter Particles (WIMPs) are among the most well-motivated models for particle dark matter. While these particles can be detected through direct, indirect, or collider experiments, only their indirect annihilation produces a guaranteed signal. Intriguingly, experimental searches using both gamma-rays and cosmic-rays are beginning to close in on this coveted "thermal annihilation cross-section". Intriguingly, several excesses in Galactic center gamma-rays and cosmic-ray antiprotons have been discovered. Even more intriguingly, these excesses may be consistent with each other. In this talk, I will summarize the current state of the field, and argue that there is hope of resolving this puzzle within the next five years.
at 15. If you would like to suggest a seminar speaker or want to be added to the email list, please contact the organizer (Raphael.Mignon-Risse@ntnu.no).
The (planned) seminars in 2024 are
- 06.02. Michael Unger (KIT and IFY, NTNU): News from the Galactic Magntic Field (...and the Origin of the Amaterasu Particle)
Abstract: Galaxies are known to be permeated by large-scale magnetic fields with energy densities comparable to the turbulent and thermal energy densities of the interstellar medium. A good knowledge of the global structure of these fields is important to understand their origin and to infer their effect on galactic dynamics and the propagation of charged particles in galaxies. In this talk I will present new studies of the global structure of the magnetic field of our Galaxy based on the analysis of recent new full-sky data of extragalactic rotation measures and the final polarized intensity maps from WMAP and Planck. The analysis employs the latest models for the thermal electron density tuned to the dispersion measures of Galactic pulsars and state-of-the-art cosmic-ray electrons models, needed to predict the rotation measures and synchrotron emission from the Galaxy, respectively. As a result, I will present a major revision of the widely-used Jannson-Farrar 2012 model of the magnetic field of the Galaxy. In addition to a fiducial magnetic field model, a suite of alternative models was studied that fit the data with similar quality, but use different model assumption. This suite of models is then used to place a lower limit on the model uncertainties. As an application, I will discuss the uncertainties of the predicted deflection of ultrahigh-energy cosmic rays in the Galaxy, in particular the origin of the extremely energetic "Amaterasu particle" recently reported by the Telescope Array Collaboration.
slides
- 13.02. Lena Saurenhaus (MPP Muenchen): Seyfert Galaxies as Astrophysical Neutrino Sources
Abstract: Active galactic nuclei (AGNs) are among the most powerful objects in the Universe and are suspected to be sources of astrophysical neutrinos. Recently, the IceCube Collaboration reported an excess of neutrino events with energies between 1.5 and 15 TeV associated with NGC 1068, a nearby Seyfert galaxy with an extraordinarily high intrinsic X-ray flux. The lack of observable gamma rays in this energy range indicates that these neutrinos are likely to be produced in the AGN corona, which is opaque to high-energy gamma rays. I will give an overview over existing neutrino emission models for NGC 1068-like sources and talk about our current project, which explores the prospects of observing other hidden neutrino sources with similar neutrino production mechanisms and aims to constrain their contribution to astrophysical neutrino observations.
slides
- 05.03. Triantafyllos Kormpakis (IFY, NTNU): The Particle in Cell method: Theory and astrophysical applications
Abstract: The Particle in Cell (PIC) numerical method (first developed in the 1950s) aims to simulate the behavior of plasmas in the presence of electric and magnetic fields. With it's unique architecture, moving particles on a Langrangian frame and depositing their charge and current densities on a fixed eulerian mesh, it tracks the evolution of systems where high densities of charged particles (mainly electron-positron pairs) and/or strong electromagnetic fields are present. In the parameter space where the Force free magnetic field approximation is valid, such as the magnetospheres of pulsars, magnetars and active galactic nuclei (AGN) jets, the PIC scheme accurately simulates features such as magnetic reconnection phenomena, enables the study of shock acceleration, particle flows and emission regions. In this talk I will first give a basic overview of the PIC method, particularly in its implementation on the Zeltron code. This will lead to the discussion of my application and qualitative reproduction of existing results, in magnetic reconnection in ABC magnetic fields (particular eulerian flows with stable as well as chaotic flow regimes). Lastly, I will also describe my application and results of PIC methodology to a test case: an axially symmetric magnetic field, representing a magnetic field topology present in an AGN jet.s.
slides
- 14.03. Rita C. Anjos (U Parana): The nature of high-energy multi-messenger sources
Abstract: In this seminar, I will present the main results of high-energy physics, considering charged particles and gamma radiation as multi-messengers. In this context, the primary sources of these particles will be discussed, along with significant challenges in the field and some results from my research group in Brazil. I will also introduce some diversity/outreach initiatives developed by the group to foster the inclusion of children and youth in the subatomic universe.
slides
- 19.03. Ellis Owen (U Osaka): Cosmic Ray feedback in galaxy evolution
Abstract: Cosmic rays go hand-in-hand with violent and energetic astrophysical conditions. They are an active agent within galactic and circumgalactic ecosystems, where they can deposit energy and momentum, modify the circulation of baryons, and even have the potential to regulate star-formation on local and galactic scales. Their influence in galaxies can be probed using observable signatures across the electromagnetic spectrum, with high energy radiation being particularly important to determine their energy budget, feedback power and hydrodynamic effects. In this talk, I will discuss some of the astrophysical impacts hadronic and leptonic cosmic rays can have in and around galaxies, how their influence can be probed using signatures in X-rays and gamma-rays, and the opportunities soon to open-up that will allow us to map-out the multi-scale effects of cosmic rays in galaxies near and far.
slides
- 21.03. Dmitri Semikoz (APC Paris): Multi-messenger signatures of astrophysical neutrino sources
Abstract: In this talk I’ll review recent observations of galactic and extragalactic neutrino sources comparing them to the predictions of theoretical models. At multi-TeV energies dominant contribution to the neutrino flux of Milky Way is expected from Galactic Ridge, brightest region of our Galaxy, where cosmic rays interact with interstellar gas and produce secondary gamma-rays and neutrinos. In neutrinos first hint of Galactic Ridge was found in ANTARES in 2022. In 2023 IceCube detected it in cascade channel with 4 sigma significance. I’ll discuss perspectives of detection of Galactic Ridge by future neutrino telescopes and by LHAASO, SWGO and CTA in gamma-rays. Also I’ll review recent gamma-ray and neutrino observations from Pevatron source in Cygnus region.For extragalactic neutrino sources I’ll focus on Seyfert galaxies. In addition to well known NGC 1068 only two other sources, based on their hard X-ray properties, NGC 4151 and NGC 3079 are expected to be detectable in 10 years of IceCube data. We find an evidence for neutrino signal from both sources in publicly available ten-year IceCube dataset. The chance coincidence probability to find the observed neutrino count excesses in the directions of the two out of two expected sources, in addition to the previously reported brightest source, is p<2.6e-7. This corresponds to the detection of Seyfert galaxies as a neutrino source class.
slides
- 25.06. Paul Lai (University College London): Tracking the gas distribution in the Galactic Centre using neutrinos and Alisha Roberts (IFY, NTNU): Investigating Neutrino Emissions from Blazar 3C 454.3
- tbd. Jens Oluf Andersen (IFY, NTNU): Pion condensation and pion stars
Abstract: In this talk I will discuss pion condensation in the context of two and three-flavor chiral perturbation theory. I will present results for quark and pion condensates as functions of the isospin chemical potential. The results compare favorably to those of lattice QCD. As an application, I will discuss pion condensation in a dense neutrino cloud and the possibility of pion stars. These are compact objects with a mass up to 20 solar masses and radii of up to 140km. 30.10.2020, Angelo Ricciardione (INFN Padua): Characterization of Cosmological Gravitational Waves with the LISA Detector - 22.1.2021, Marco Muzio (NYU)
Germano Nardini (UiS)
- Alexander Stasik (UiO)
Abstract: Primordial Gravitational Waves (GWs) represent a key test of inflation and they are a unique tool to explore the physics and the microphysics of the early Universe. After the GW detections by the LIGO/Virgo collaboration the next target of modern cosmology is the detection of stochastic background of GWs. Even if the main probe of primordial GWs is the Cosmic Microwave Background, we will see in this talk how we can extract information about primordial GWs at smaller scale. In particular the space based LISA interferometer, in addiction to detection and characterization of GWs of astrophysical origin, will give compelling information about the cosmological background of GWs. In this talk I will summarise part of the activity developed within the LISA Cosmology working group, and, in particular, I will discuss on the ability of LISA to test primordial well motivated model of inflation and I will discuss about peculiar features of the SGWB, like anisotropy and non-Gaussian
20.11.2020, Tor Nordam (NTNU) : Eulerian and Lagrangian methods for advection-diffusion problems
Abstract: In applied environmental science, such as oceanography and meteorology, transport problems are a common topic. The focus could be the movement of the ocean and atmosphere themselves, or transport of other substances such as pollutants, algae, fish eggs, etc. Different numerical approaches are used, and it is common to separate between Eulerian methods, where you solve the advection-diffusion PDE directly, and Lagrangian methods, where you simulate the random motion of an ensemble of "particles". The idea in the latter case is that the distribution of particles should evolve like the distribution described by the PDE. Mathematically, Lagrangian methods are numerical solutions of a Stochastic Differential Equation (SDEs), whose Fokker-Planck equation is the advection diffusion equation. In this talk, I will describe and illustrate the Eulerian and Lagrangian approaches, using simple 1D examples. I will discuss strengths and weaknesses of the two different approaches, and the conditions that must be satisfied for the two approaches to be equivalent. Finally, I will present some "pitfalls", where a naïve approach can lead to wrong answers.